Many medications are provided in fixed dosage cartridge-needle units. Cartridge-needle units include a glass barrel to which a needle assembly is mounted at one end. The barrel is filled with a medicine. The medicine is held within the barrel by a piston at one end and, typically, a rubber diaphragm at the needle end. The needle assembly is typically mounted to a necked down region of the barrel by a hub. The inner end of the needle is mounted within the hub to a position just opposite the rubber diaphragm. To activate the cartridge-needle unit, the barrel and needle assembly are pushed towards one another so that the inner end of the needle punctures the diaphragm to allow the medicine within the barrel to flow through the needle.
Cartridge-needle units are commonly used with a reusable holder. Holders have a body within which the cartridge-needle unit is placed. The holder includes a stem or plunger which is mounted, typically threaded, to the piston. The sheath covering the needle is removed and the injection is given. After use, the plunger is uncoupled from the piston and the used cartridge-needle unit is removed from the body and disposed of.
While the use of cartridge-needle units has many advantages, there are drawbacks as well. Several cartridge-needle units are generally packaged in a tamper resistant container. Often the container will use a metal shield at the plunger ends of the barrels to keep unscrupulous individuals from surreptitiously gaining access to the contents of the unit. The special packaging used is relatively costly and increases the actual cost of each cartridge-needle unit. Further, the present systems are not well suited for preventing inadvertent needle sticks, a serious health concern.